Retirement Question????

Hi all, I am wondering if some of you out there can give some retirement advice and information.
Basically, I am wondering when one knows that they have enough to retire. What advice/formulas, books or experts (besides DR) have you been using to make that decision. One big concern will be Health insurance.

My DH and I are still in our 40’s, but we have been saving since we left college and have never really carried a debt outside our mortgage. We have money saved for retirement, investments, and kids college. Our only debt is our mortgage which has an excellent rate (less than 3%) and we owe less than 30% of its value.

I’m just wondering how to know when enough is enough and what our goals should be.